Evaluation of mechanical properties of thin films used in semiconductor processing such as, for example, residual stress, CTE (coefficient of thermal expansion) and Young's modulus, is critical for the understanding of the performance (both mechanical and electrical) of the materials used. As the mechanical properties can significantly vary from wafer to wafer, and with process conditions, obtaining a clear understanding of the effects of processing is very valuable to understanding yield and performance. Currently, the processes in which these films are tested and characterized are quite rudimentary and labor intensive.
By creating free-standing film structures, which are released from the substrate to form suspended devices such as cantilever and bridges, using micro-machining techniques, and or processing, the mechanical properties of the film can be accurately determined. This approach has been extensively researched in the semiconductor industry, and as an example, NIST (National Institute of Standards and Technology) has developed three standards for the determination of intrinsic stress and characterization of elastic properties in very large scale integration (VLSI) thins films. This is reported, for example, in D. Herman, M. Gaitan, D. Devoe, “MEMS Test Structures for Mechanical Characterization of VLSI Thin Films”, Proc. SEM Conference, Portland, Oreg., Jun. 4–6, 2001. See also http://mems.nist.gov/.
However, procedures described above have been developed for conventional films used in VLSI/CMOS (complementary metal oxide semiconductor) technology whereas low k dielectric films (having a dielectric constant of less than silicon dioxide, SiO2) are very sensitive to most common chemicals and gases used in standard micro-machining processes. Subsequently, the low k films will not typically survive the general micro-machining sacrificial etch and release techniques widely used. See, for example, U.S. Pat. No. 6,808,205 to Jang, et al. and U.S. Pat. No. 6,666,979 to Chinn, et al, which describe typical micro-machining sacrificial etch and release techniques.
In view of the above, there is a need for providing a method for the micro-machining of low k films, which minimizes the problems of patterning and releasing chemically sensitive low k films, without the complication of a permanent hardmask stack. Moreover, there is a need for providing a method that yields unaltered free-standing structures.